1. Field of the Invention
The present invention relates to glow discharge systems and methods, and more particularly, to increasing the amount of electrons in the plasma glow region of a glow discharge system by radiation by photons such as by using a laser beam to enhance the intensity of the glow for improved etching/deposition processes.
2. Description of the Prior Art
The prior art contains references wherein radiation such as by laser beams are used in combination with plasmas for various diverse purposes.
U.S. Pat. No. 3,723,246 issued Mar. 27, 1973 to Lubin, entitled PLASMA PRODUCTION APPARATUS HAVING DROPLET PRODUCTION MEANS AND LASER PRE-PULSE MEANS describes an apparatus and method for producing a freely expanding high temperature plasma from a high density target that is irradiated with laser light by a tailored laser pulse. Means are described for producing a tailored laser light pulse and a tailored target for producing a laser-target interaction.
U.S. Pat. No. 3,826,996 issued July 30, 1974 to Jaegle et al entitled METHOD OF OBTAINING A MEDIUM HAVING A NEGATIVE ABSORPTION COEFFICIENT IN THE X-RAY AND ULTRAVIOLET SPECTRAL RANGE AND A LASER FOR PRACTICAL APPLICATION OF SAID METHOD, a plasma is formed from a material in which the ions possess discrete metastable energy states interacting with the energy states of the continuum which are populated by the free electrons of the plasma. Population inversion is achieved between a number of these metastable states and states of lower energy, negative absorption being then produced for the transition which couples the metastable states with said states of lower energy.
In order to form the plasma, a giant-pulse laser beam is caused to interact in vacuum with a solid target formed of said material and is focused within the target near the surface through which the beam passes, the beam power being such as to ensure sufficiently populated metastable states of the ions of the material.
U.S. Pat. No. 4,152,625 issued May 1, 1979 to Conrad, entitled PLASMA GENERATION AND CONFINEMENT WITH CONTINUOUS WAVE LASERS describes a method and apparatus for initiating a stable plasma and maintaining the plasma stationary. A high power, continuous wave laser is used to initiate and maintain the plasma, while a magnetic trap confines the plasma.
In U.S. Pat. No. 4,189,686 issued Feb. 19, 1980 to Brau et al entitled COMBINATION FREE ELECTRON AND GASEOUS LASER describes a multiple laser having one or more gaseous laser stages and one or more free electron stages. Each of the free electron laser stages is sequentially pumped by a microwave linear accelerator. Subsequently, the electron beam is directed through a gaseous laser, in the preferred embodiment, and in an alternative embodiment, through a microwave accelerator to lower the energy level of the electron beam to pump one or more gaseous lasers. The combination laser provides high pulse repetition frequencies, on the order of 1 kHz or greater, high power capability, high efficiency, and tunability in the synchronous production of multiple beams of coherent optical radiation.
The publication LASER-PLASMA INTERACTIONS FOR THE DEPOSITION AND ETCHING OF THIN-FILM MATERIALS by Philip J. Hargis, Jr. and James M. Gee, Solid State Technology/Nov. 1984, pp. 127-133, states that laser-plasma chemical processing is a new materials processing technique in which both ultraviolet laser irradiation and a glow discharge are required for deposition or etching. This versatile materials processing technique was used to deposit silicon and etch a number of insulators. The process was also used to deposit epitaxial silicon films on single-crystal silicon wafers. Deposited and etched films were characterized by laser Raman spectroscopy, transmission electron microscopy, and scanning electron microscopy. Results obtained to date have been interpreted in terms of a mechanism that involves interaction of the incident ultraviolet laser radiation with a plasma deposited absorbed layer on the substrate.
In an other publication by J. M. Gee, P. J. Hargis, Jr., M. J. Carr, D. R. Tallant and R. W. Light entitled PLASMA-INITIATED LASER DEPOSITION OF POLYCRYSTALLINE AND MONOCRYSTALLINE SILICON FILMS, Mat. Res. Soc. Symp. Vol. 29 (1984) published by Elsevier Science Publishing Co., Inc., the authors report a new method of silicon deposition using the interaction between the radiation from a pulsed-ultraviolet excimer laser and the plasma species produced in a glow discharge in silane (SiH.sub.4). Examination of the deposited film by laser Raman spectroscopy and by transmission electron microscopy revealed that the morphology ranged from polycrystalline silicon at laser fluences of 0.13-0.17 J/cm.sup.2 to epitaxial silicon at fluences of 0.4-0.6 J/cm.sup.2. Growth rates of 100 nm/min for polycrystalline silicon and 30 nm/min for monocrystalline silicon were achieved.
The Hargis and Gee publication and Gee et al publication, referred to above, do not anticipate the present invention. Both of these papers cover the same work on photo enhanced chemical vapor deposition. Their work shows the laser radiation interacts with an absorbed layer deposited by the plasma. They also show the laser radiation does not interact with the plasma. The electron-hole plasma discussed in their paper exists in the deposited layers only. It is a change in the electronic distribution of the solid that drives a chemical reaction.
A very recent publication, LASER-INDUCED PLASMAS FOR PRIMARY ION DEPOSITION OR EPITAXIAL Ge AND SL FILMS (J. Vac. Sci. Technol. B. Jul./Aug., 1985, pp. 968-974) is also of interest but does not anticipate the present invention. Lubben et al use the material ablated by laser radiation to deposit a film. They discuss the generation of the neutral plasma caused by the interaction of the laser radiation with the ablated material. The present invention deals with the enhancement of a plasma by the generation of photoelectrons using UV radiation.
In the publication by Gail A. Massey entitled "Laser Photoelectron Sources of High Apparent Brightness", published in IEEE Journal of Quantum Electronics, Vol., QE20, No. 2, Feb. 1984, the author states that by focusing an ultraviolet laser beam to a small spot on an appropriately shaped cathode, one can obtain photoelectron beams of increased brightness. Such a continuous electron source may be useful in electron beam lithography and other applications.